14.6 Cercospora (Ascomycota)

Many species of this genus cause plant diseases, mostly of the ‘leaf
spot’ variety. Leaf spots are rounded blemishes occurring on the leaves
of the infected plants; a typical spot has a defined edge with a darker border
and a central zone varying from yellow to brown. Numerous spots can merge
together and the larger areas can be called blights or blotch
diseases.

Cercospora beticola is the most destructive leaf disease of sugar
beet worldwide; the disease reduces yield and quality of sugarbeet and the need
to use fungicide to control leaf spot disease adds significantly to the cost of
production. C. beticolaoverwinters as stromata in
infected crop residues and spores produced on these are the prime source of
infection of the leaves of the next season’s crop (Khan et al., 2008).

Disease control strategies rely on a combination of fungicide
applications (alternating and combining fungicides differing in modes of
action to avoid resistance development in the fungus), growing resistant
cultivars, and appropriate crop rotation (to avoid the overwintering
stromata).

Improvement of these integrated pest management systems is the main hope,
now, for more effective and environmentally sound disease control. Plant
varieties with greater genetic resistance is central to this, but
pathogen-resistant strains often have lower yields in the absence of the
disease, which is unacceptable in commercial practice. Promisingly, yield
performance of recently isolated sugar beet varieties with resistance to
Cercospora beticola have equalled yields of susceptible varieties and
should allow reduced fungicide to be use in integrated pest management
programmes (Skaracis et al., 2010; Vogel et al., 2018).

Resources Box 14.1

Where to find more information about crop
diseases, crop losses, plant pathogens
and food and agriculture statistics

We have a page giving references to
scientific papers and hyperlinks to online resources.